A voltage-increased type electro-optical Q-switched pulse laser generally includes a gain medium 5, an input coupler 4, an output coupler 9, a Pockels cell 7, a quarter-wave plate 8, a polarizer 6, and a pump source 1, and these elements are shown, for example, in FIG. 1 (which illustrates laser equipment that may also be used to perform the methods of the present invention described in further detail below). The angle between a principal axis of the quarter-wave plate 8 and a transmissive direction of the polarizer 6 is 45°. The Pockels cell 7 and the quarter-wave plate 8 form an electro-optical Q switch, which is used for controlling the polarization direction of an intracavity laser beam. When the voltage from an electro-optical Q-switch driver module 3 is set as 0 and applied to the Pockels cell 7, the polarization direction of the intracavity laser beam rotates by 90° after passing through the Q switch two times, and the resonator is in a high-loss state. In this case, the pump energy is absorbed by the laser gain medium 5 leading to an accumulation of inverted populations. When the inverted populations reach the maximum, a square-wave signal whose peak voltage is equal to the quarter-wave voltage of the Pockels cell 7 is used, to thereby obtain a giant pulse laser output.
To obtain a pulse laser with sub-nanosecond level pulse width, both a short rising edge time and a short high-level voltage duration of the square wave driving signal are required. However, in practice, the Q-switch driver module 3 with a rising edge time of a few nanoseconds always needs to keep a specific high level duration, which makes a part of laser photons oscillate back and forth in the resonator. As a result, the falling edge time of a laser pulse is prolonged, and the laser pulse width is increased (e.g., beyond the sub-nanosecond level).
To decrease the pulse width of a laser pulse, the following technologies are generally used: shortening resonator length, increasing transmittance of output coupler, active/passive dual Q-switching, and the like. Each of these methods has failed to reliably decrease the pulse width to beyond the sub-nanosecond level. Because the resonator length is limited by sizes of gain medium and other intracavity components, it is difficult to build a sub-nanosecond high-energy laser operating at a high repetition frequency when the method of using a short resonator is used. When the method of increasing transmittance of output coupler is used, the laser pulse width can be decreased by increasing pump power, but there remain problems with such a method, including potential thermal damage of a laser crystal due to a relatively high threshold, and widening of the rising edge of a laser pulse due to high loss. In the active/passive dual Q-switching method, an additional element needs to be inserted into the resonator, and consequently, the resonator length is increased, and it is also relatively difficult to implement output of a sub-nanosecond laser.
Therefore, it would be desirable to overcome these issues in known methods of forming a laser, such that a sub-nanosecond pulse laser is reliably generated.